. And one of his closest friends in Congress suggested he should step down if it is in the best interest of Wu's family and future.

Wu announced late Sunday through an intermediary that he wanted to finish his term and retire, meaning he would remain a member of Congress until the end of 2012. That decision drew an immediate response from Pelosi, who formally asked Monday for a full-throated ethics investigation of the case.

Rep. John Larson, D-Conn., who was elected the same year as Wu and is a key leadership aide to Pelosi, spoke with Wu for 40 minutes just off the House floor on Monday.

Larson said that Wu did not deny the sexual encounter with the 18-year-old, who is the daughter of one of Wu's childhood friends, but insisted he "did nothing illegal" and will eventually be "vindicated."

"What he said to me is, he's taking it one day at a time, and I said, 'Dave, you have to do what's in the best interest of your young family and yourself and then the institution, in that order'." Larson said in an interview.

"He said this was weighing heavy on his mind and he hadn't made up his mind. He was obviously quite troubled by the whole thing and insisting that when everything comes out, 'I'll be vindicated.' I told him, 'Dave, there are no good answers to this,'" said Larson, the No. 4 ranking official in the Democratic leadership.

Larson added that Wu said he "did not use good judgment" during the encounter in Orange County, Calif.

But while others spoke about the incident and what it means, Wu spent the entire day largely out of sight, remaining in the Democratic cloakroom just off the House floor for the entire day. He only emerged to vote.

Wu left the Capitol shortly after 7 pm, followed by reporters for The Oregonian and other outlets.

Wu ignored reporters' questions as he left the Capitol, declining to explain why he has not decided to resign or the reasoning for his announcement to finish his current term and retire in 2012.

As he stepped into the car, however, he stopped when asked if he thought he would be vindicated.

"Aside from everything else, I am trying to take care of the interests of my family," Wu said before driving off. Wu has yet to offer a public explanation or defense for his actions over Thanksgiving. Prior to his brief comment Monday, Wu issued a single sentence Friday night in response to questions.

"This is very serious, and I have absolutely no desire to bring unwanted publicity, attention, or stress to a young woman and her family," he said.

"I agree with Leader Pelosi that the Ethics Committee must look at this and must look at it at an accelerated fashion," he said. "There has been an allegation made and we need to know the merits of that allegation."

Whatever ability Wu has may be diminished as the Ethics Committee probe takes shape.

The committee has broad powers to subpoena witnesses as well as "books, records, correspondence, memoranda, papers, documents, and other items as it deems necessary." It can hold public hearings and also has power to expand its probe to other potential violations. Sources say that could be troublesome because Wu has allegedly used congressional staff for such private work as managing his household finances.

Lines of inquiry likely would bleed into Wu's other behavior during the 2010 campaign season, including an admission that he took prescription painkillers from a campaign donor.

"There's an allegation here and the ethics committee would look into that, but of course there's background in the rather strange behavior that Wu exhibited about seven or eight months ago," said Bill Lunch, an Oregon political analyst. "All of this is likely connected in trying to assess the state of his mind or his mental stability."

Still, even if the committee finds some wrong doing, it's limited in what it can suggest as a punishment, Lunch said. "The ethics commission doesn't have a lot of power; it can't remove a member from Congress.

"This is an attempt to put pressure on him to resign. They'd like to have him gone," Lunch said. "The fact that Pelosi has gone public with the request for an ethics investigation is an indication of some of the things going on beneath the surface."